Recognition/anti-collision light for aircraft

ABSTRACT

A recognition light includes a reflector having an axis and first and second annular semi-parabolic reflective surfaces which have respective focal points axially spaced apart from one another, and first and second annular lamps respectively disposed at the focal points. A cover surrounds the reflector and lamps and includes a lens for focusing the light along a plane perpendicular to the axis of the reflector, the lens including first and second Fresnel lens portions each including a convex lens and a prism lens, the convex lenses being disposed adjacent one another and transaxially aligned with the first and second lamps, respectively. A light detector detects light emitted from at least one of the lamps, a monitor circuit provides a fail signal when a characteristic of the light output of at least one of the lamps does not satisfy a specified criteria, and a control circuit first activates the first lamp and then the second lamp in response to receipt of the fail signal of the monitor circuit.

This application is a divisional of U.S. patent application Ser. No.09/187,495, filed Nov. 6, 1998, now U.S. Pat. No. 6,278,382.

FIELD OF THE INVENTION

The present invention relates to recognition/anti-collision lights and,more particularly, to a method and apparatus for extending the usefullife of such lights and/or for detecting the failure of such lights.

BACKGROUND OF THE INVENTION

Recognition/anti-collision lights are used on aircraft to produce brightflashes of light readily visible to the human eye for improvingrecognition of the aircraft from the ground or from other aircraft. TheFAA (Federal Aviation Administration) currently mandates that aircrafthave such lights with an acceptable minimum effective light intensity of100 or 400 candela (depending on the aircraft) when viewed within fivedegrees of a horizontal plane.

Many prior art recognition/anti-collision lights include a flashtube, orstrobe light, that initially produces a light intensity that meetsgovernment guidelines. However, the light intensity of the flashtubegradually degrades with use over time and eventually falls below theminimum intensity requirements, thereby requiring servicing and/orreplacement of the flashtube. The mean time between failure (MTBF) of atypical flashtube is about 1500-3000 hours.

Anti-collision lights are therefore periodically tested, in someinstances with elaborate equipment, to ensure that they meet the FAArequirements. A common practice has been to replace the lights on ascheduled basis to ensure proper illumination requirements are met eventhough many of the lights still satisfy illumination requirements.

In order to reduce the frequency at which a recognition/anti-collisionlight requires replacement, it would be desirable to have ananti-collision light with an improved (increased) mean time betweenfailure (MTBF).

SUMMARY OF THE INVENTION

The present invention provides a recognition/anti-collision lightincluding, in a preferred embodiment, two flashtubes and a controlsystem that sequentially operates the two flashtubes in order to extendthe overall useful life of the light. The invention also provides atechnique for extending the life of a single flashtube or multipleflashtubes.

According to one aspect of the invention, a recognition light comprisesa reflector having an axis and first and second annular semi-parabolicreflective surfaces which have respective focal points axially spacedapart from one another, and first and second annular lamps respectivelydisposed at the focal points.

According to another aspect of the invention, a recognition lightcomprises a parabolic reflector, first and second annular lampssurrounding the reflector, and a lens cover surrounding the reflectorand lamps, the lens cover including a lens for focusing the light alonga plane perpendicular to the axis of the reflector, the lens includingfirst and second Fresnel lens portions each including a convex lens anda prism lens, the convex lenses being disposed adjacent one another andtransaxially aligned with the first and second lamps, respectively.

According to another aspect of the invention, a recognition lightcomprises first and second lamps, a light detector positioned to detectlight emitted from at least one of the lamps, a monitor circuitconnected to the light detector for providing a fail signal when acharacteristic of the light output of at least one of the lamps does notsatisfy a specified criteria, and a control circuit connected to themonitor circuit and the first and second lamps for first activating thefirst lamp and then the second lamp in response to receipt of the failsignal of the monitor circuit.

According to another aspect of the invention, a recognition light of anaircraft comprises a flashtube, a light detector positioned to detectlight emitted from the flashtube, a monitor circuit connected to thelight detector for measuring the intensity of the detected light andcomparing the measured intensity with a reference value corresponding toa predetermined light intensity level, and a control circuit connectedto the flashtube and monitor circuit for flashing the flashtube at afirst power level and then at an increased power level when the measuredintensity drops below the reference value, thereby to increase theintensity of the flashes emitted by the flashtube to above thepredetermined light intensity level.

According to another aspect of the invention, a method for increasingthe useful life of a recognition light of an aircraft comprises flashinga flashtube, monitoring the light output of the flashtube, comparing themeasured light output of the flashtube with a reference valuecorresponding to a predetermined light intensity value, increasing thepower delivered to the flashtube when the measured light output dropsbelow the reference value, thereby to increase the intensity of theflashes emitted by the flashtube to above the reference value.

According to a further aspect of the invention, a method for monitoringthe useful life of an aircraft recognition light comprises flashing aflashtube, and monitoring the light output of the flashtube with a lightdetector that converts the detected light output into an integratedoutput voltage corresponding to the light output of a plurality offlashes of the flashtube.

According to another aspect of the invention, a method for increasingthe useful life of a recognition light comprises providing first andsecond lamps, operating the first lamp, monitoring a characteristic ofthe light output of the first lamp and providing a fail signal when thecharacteristic of the light output of the first lamp does not satisfy aspecified criteria, and stopping operation of the first lamp andoperating the second lamp in response to receipt of the fail signal.

According to another aspect of the invention, a method for providingvisual notification of required replacement of an anti-collision lightprior to failure of the anti-collision light, comprises providing ananti-collision light including a lamp, operating the lamp at a firstflash rate at a light intensity above a predetermined light intensityvalue, and operating the lamp at a second flash rate distinguishablefrom the first rate when the light intensity of the lamp approaches thepredetermined light intensity value.

According to yet another aspect of the invention, a lamp fixturecomprises an annular reflector and first and second annular lampssurrounding the reflector, and the reflector having a reflector surfaceconfigured to reflect light outwardly from the lamp fixture from both ofthe lamps.

The foregoing and other features of the invention are hereinafter fullydescribed and particularly pointed out in the claims, the followingdescription and the annexed drawings setting forth in detail one or moreillustrative embodiments of the invention, such being indicative,however, of but one or a few of the various ways in which the principlesof the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a light intensity monitoring systemconstructed in accordance with the present invention.

FIG. 2 is an exploded perspective view of the light of FIG. 1.

FIG. 3 is a cross-sectional view of the light of FIG. 1.

FIG. 4 is an exploded perspective view of the light fixture assemblyincluded in the light of FIG. 1.

FIGS. 5 and 6 are interrelated functional block diagrams of theelectrical circuitry used in the light of FIG. 1.

DETAILED DESCRIPTION

Referring now in detail to the drawings, and initially to FIGS. 1-3, alight constructed in accordance with the present invention is generallyindicated at reference numeral 10. The light 10 was developed for use asan aircraft recognition/anti-collision light and is herein describedchiefly in this context. However, those skilled in the art willappreciate that a light according to the invention will have otheruseful applications including but not limited to uses in other types ofvehicles, in industrial applications, etc. It should be appreciated thatsuch alternative applications are contemplated as falling within thescope of the present invention. It also should be appreciated thatreferences herein to top and bottom, upper and lower, etc., are made inrelation to the illustrated orientation of the light to describepositional relationships between components of the light and not by wayof limitation, unless so indicated. Also, the terms “recognition” and“anti-collision” are used interchangeably.

As shown in FIGS. 1-3, the anti-collision light 10 includes a housing 12composed of upper housing member or cover 14, a lower housing member orcase 16, and a mounting plate 18 disposed between the cover 14 and case16. The cover 14 is transparent and preferably has a Fresnel lens 20integrally formed therein. The cover, which may also be provided with aconventional drain plug 22, is secured to the top side of the mountingplate 18 by a hold-down ring or lens bezel 24. The case 16 is fastenedto the underside of the mounting plate 18 by fasteners (not shown) orother suitable means. Together, the cover 14, case 16 and mounting plate18 define an interior region 26 for containing the internal componentsof the light 10, which internal components generally comprise aflashtube fixture assembly 28, a fixture base 30 and electrical circuitcomponents 32 for supplying power to and controlling the flashtubefixture 28.

As seen in FIG. 3, the flashtube fixture assembly 28 includes twoflashtubes 34 and 36 and a common spool-shaped reflector 38. Thereflector 38 includes upper and lower reflector half spool members 40and 42 that are axially aligned and coupled together. The reflector 38is coupled to the fixture base 30 which, in turn, is fastened to themounting plate 18.

The flashtubes 34 and 36, which are herein referred as a main or primaryflashtube and a spare or secondary flashtube 36, respectively, areconventional circular-shaped (annular) flashtubes that are disposedcircumferentially around the waist (smallest diameter portion) of thespool-shaped common reflector 38 in substantially parallel relation toone another. The main flashtube (or spare flashtube) 34 can be eitherthe upper or lower flashtube shown in the illustrated light. Theflashtubes 34, 36 preferably are supported in spaced apart parallelrelationship, such as by respective centering spacers 44.

With additional reference to FIG. 4, the centering spacers 44 havecentral disk portions 46 from which support arms 48 radiate. As shown,four circumferentially equally spaced apart support arms 48 may beprovided for each spacer. The radially outer ends 50 of the support arms48 are contoured to support the corresponding flashtube 34, 36 and eacharm 48 may have a hole 52 and slot 54 therein for receipt of a wire (notshown) wrapped around the flashtube 34, 36 to hold it to the support arm48 and thus to the centering spacer 44. Each centering spacer 44 isaffixed to the narrower end of a corresponding one of the upper andlower reflector halves 40 and 42 by suitable fastening means such asscrews 60. Other, or alternative, types of spacers may be employed tosupport and maintain a spaced relationship between the main flashtube 34and spare flashtube 36.

The upper and lower reflector halves 40 and 42 progressively decrease indiameter (width) going from their axially outer ends to their axiallyinner ends that are butted together at the waist 66 of the hourglassshape reflector 38. Each reflector member 40, 42 has an interior annularregion (chamber) 68, 70 disposed between a radially outer wall 72, 74and an interior center post 76, 78. The interior annular chamber 68, 70is closed at the axially inner end of the reflector member 40, 42 by anaxial end wall 80, 82 while the other end of the reflector member 40, 42has an opening 84, 86 through which a trigger inductor assembly 88, 90(FIG. 4) can be inserted into the interior region 68, 70. The triggerinductor assembly 88, 90 includes a PTFE inductor housing 96, 98containing a trigger inductor 100, 102. The trigger inductor 100, 102 iselectrically connected by leads (not shown) to terminal ends 104, 106 ofthe corresponding flashtube 34, 36. The terminal end portions 104, 106extend perpendicularly to the plane of the otherwise annular flashtubes34, 36. The terminal end portions 104, 106 extend through an opening 108(only one of which is shown) in the radially outer wall 110, 112 of thereflector half 40, 42 and into the interior region 68, 70. After theelectrical connections have been made, preferably the terminal ends 104,106 and trigger inductor assemblies 88, 90 are potted into theirrespective interior region 68, 70 with a suitable potting compound.

Together each flashtube 34, 36, reflector half 40, 42 and triggerinductor assembly 88, 90 form a respective light module 114, 116. In theillustrated embodiment the light modules 114 and 116 are substantiallyidentical except for their electrical connections. The trigger inductormodule 90 and flashtube 36 of the lower light module 116 areelectrically connected to a printed circuit board 118 fixed to thebottom (axially outer) end of the reflector half 42. The bottom printedcircuit board 118 is provided with pins 120 to form a plug that mateswith a corresponding socket (not shown) in the fixture base 30.

The bottom printed circuit board 118 also has through pins connected toan upper printed circuit board 126 at the axially inner end of the lowerlight module 116. The upper printed circuit board 126 is provided withpins 128 for mating with sockets provided on a printed circuit board 132fixed to the bottom (axially inner) end of the upper light module 114.The sockets are electrically connected to the trigger inductor module 88and flashtube 34, and any other supporting electrical circuitry may beprovided on a printed circuit board 134 fixed to the top (axially outer)end of the upper light module 114.

With the foregoing preferred construction of the light fixture 28, thelight fixture 28 is assembled by plugging the upper and lower modules114, 116 together and the lower module 116 to the fixture base 30. Whenthus assembled, the upper and lower light modules 114 and 116 may beheld securely together and to the fixture base 30 by a bolt (not shown)that extends through the center tube 76, 78 and has its lower endthreaded into the fixture base 30, such as into a nut fastener attachedto the underside 136 of the top wall 138 of the fixture base 30 or byany other suitable means.

In view of the foregoing, it can be seen that the modular constructionof the light 10 facilitates replacement of a defective and/or worn outmodule 114, 116, as well as assembly of the light fixture 28 in thefirst instance. Together, the joined upper and lower light modules 114,116 form the reflector 38 that is shared by and thus common to the twoflashtubes 34 and 36.

The reflector 38 has an outer annular concave reflective surface 140 forreflecting light emitted by either one of the flashtubes 34, 36substantially radially (horizontally) outwardly to provide 360 degreehorizontally concentrated illumination. Preferably, the reflectivesurface 140 has upper and lower semi-parabolic shaped half surfaceportions 142 and 144 respectively formed on the upper and lowerreflector halves 40, 42. The focal points of the half portions 142, 144preferably are axially spaced apart such that the main flashtube 34 canbe positioned at one focal point and the spare flashtube 36 can bepositioned at the other focal point. Because of the annular nature ofthe reflector 38 and flashtubes 34, 36, the focal points are actuallyfocal lines with which the annular axes of the flashtubes 34, 36 arealigned. Most preferably, the semi-parabolic shaped half surfaceportions 142 and 144 each extend slightly beyond the center plane 146 ofthe respective parabola but not so far as to shade any of the reflectivesurface from light emitted from either flashtube 34, 36. Although thefocal points of the two half surface portions 142, 144 are spaced apart,they are sufficiently close to reflect and focus light emitted not onlyfrom the closest flashtube 34, 36 but also the furthest flashtube 34,36.

As will be appreciated, the light rays passing from a flashtube 34, 36to the nearest half surface portion 142, 144 of the reflector 38 will bereflected so as to pass generally radially away from the reflector 38 toprovide a horizontally concentrated light pattern. However, the lightrays passing from a flashtube 34, 36 to the furthest half surfaceportion 142, 144 will be outwardly divergent from the horizontal becausethe flashtube 34, 36 is oppositely spaced from the focal point of suchfurthest half surface 142, 144. In those applications where it isdesirable to concentrate the light intensity within a specified anglefrom horizontal, such as 5 degrees for an aircraftrecognition/anti-collision light, the cover 14 may be provided with aFresnel lens 20 (other suitable lens means or equivalent) to redirectthe otherwise wayward rays into the desired horizontal window.

As seen in FIG. 3, the Fresnel lens 20 differs from the classicalFresnel lens by having two convex lens 148, 150 at the center withprisms 152, 154 above and below. The two convex lens 148, 150 arerespectively horizontally aligned with the flashtubes 34, 36. Inessence, each flashtube 34, 36 has associated therewith a parabolicreflector 142, 144 and Fresnel lens 20, except that the portion of eachsuch reflector 142, 144 and lens 20 that would interfere with the otheris removed and the two brought together along a center plane 146 equalspaced from the horizontal planes of the flashtubes 34, 36. Of course,other shaped reflector surfaces 140 and/or lens 20 may be employed toprovide other light patterns that may be desired for variousapplications.

As depicted in FIG. 2, the flashtube fixture 28 is provided with a lightpipe (or other suitable light transmission means) 156 that extends froman aperture 158 located in the wall 74 of the reflector 38 and throughan aperture 160 in the top wall 138 of the fixture base 30. Within thebase 30, the light pipe 156 extends to a light detector 162, such as aphotodiode, mounted on a printed circuit board constituting one of theelectrical circuit components 32 (FIG. 3). The light pipe 156 attenuatesand conveys light emitted by each flashtube 34, 36 to the photodiode 162for monitoring of light intensity in the hereinafter described manner.The light intensity is monitored for the purpose of controlling theoperation of light in the following preferred manner. Preferably, thelight pipe 156 functions to calibrate the light attenuation as necessaryfor linear operation of the photodiode 162.

In operation, initially the main flashtube 34 is flashed at a desiredfrequency, such as at 42 flashes per minute which is within the flashrate range (40 to 100 fpm) mandated by FM regulations for aircraftoperation. The intensity of the flashtube 34 is monitored, preferablycontinuously, by the photodiode 162 and associated monitoring circuitry32. If the measured intensity is found not to be in compliance with apredetermined criteria, for example the measured intensity falls below aminimum specified light intensity, such as the 100 candela mandated byFAA regulations, power to the main flashtube 34 is boosted. This “powerboost” mode causes the main flashtube 34 to continue flashing above theFAA minimum effective intensity. Although this process can be repeatedmultiple times, preferably the power to the main flashtube 34 is boostedonly one time instead of incrementally.

During the main flashtube power boost mode, continuous monitoring ofintensity of the main flashtube 34 continues until once again themeasured intensity is found not to be in compliance with a predeterminedcriteria, for example the measured intensity falls below a minimumspecified light intensity, such as the 100 candela mandated by FAAregulations. At this point, flashing of the main flashtube 34 is stoppedand in its place the spare flashtube 36 is flashed. Now it is theintensity of the spare flashtube 36 that is monitored. If the measuredintensity falls below the minimum specified light intensity threshold,power to the spare flashtube 36 is boosted. This “power boost” modecauses the spare flashtube 36 to continue flashing above the FAA minimumeffective intensity.

During the spare flashtube power boost mode, continuous monitoring ofintensity of the spare flashtube 36 continues until once again themeasured intensity is found not to be in compliance with a predeterminedcriteria. At this point the spare flashtube 36 is caused to flash at adifferent rate to provide an indication that the light is close to theend of its useful life. For example, the spare flashtube 36 may becaused to flash at twice its normal frequency. Although changing theflash rate provides an effective way of indicating a need to service thelight, other indicating means may be employed such as providing anindicator light on the light unit, supplying a warning signal to theaircrafts control system for appropriate processing, such as display ona panel or screen in the cockpit, storing an indicator warning in memoryfor read-out by diagnostic equipment, etc.

The foregoing describes a preferred sequence of operation of the mainand spare flashtubes 34 and 36. However, it should be appreciated thatthe sequence may be varied and/or portions thereof used in conjunctionwith a light having more or less flashtubes. For example, the powerboost feature may be used with a single flashtube light to extend theuseful life of the light. Also, the first and second flashtubes 34, 36may be sequentially cycled through their normal power modes first, andthen cycled through their power boost modes. Moreover, the first andsecond flashtubes 34, 36 may be alternately flashed according to somespecified criteria, such as alternately for a specified period or numberof flashes. For example, the main flashtube 34 may be flashed for 1000flashes, then the spare tube for 1000 flashes, then the main tube for1000 flashes, and so on. Should either tube's light output intensityfall below the minimum, it may be operated in the power boost mode, nolonger operated, or flashed at a different rate to indicate a need forservicing.

The above described operation of the anti-collision light 10 is effectedby the electrical circuitry 32, the functional components of which areillustrated by the functional block diagrams of FIGS. 5 and 6. Theelectrical circuitry 32 according to a preferred embodiment of theinvention generally comprises power supply circuitry generally indicatedat 164 in FIG. 5, and control and monitoring circuitry generallyindicated at 166 in FIG. 6, respectively.

Referring principally to FIG. 5, the power supply circuitry 164 includesan EMI filter 168 to which input power is routed, such as 115 VACprovided on an aircraft. The EMI filter 168 attenuates noise generatedin a power supply 176 from being coupled on the aircraft power line. TheEMI filter 168 also suppresses noise on the power line that could affectthe operation of the power supply. The EMI filter 168 may be housed inan EMI can 172 provided in the housing 12 and equipped with an externalpower connector 174 as shown in FIG. 3.

The filtered power is used to power the circuits of the power supply176. The power supply 176 includes a transistor AC switch 177 whichcontrols the filtered AC power that is used for charging flashcapacitors 178. A preferred switch consists of two FET transistors in anAC bridge configuration that has slow turn-on to reduce in-rush currentwhen the flash capacitors 178 start to charge. The transistor on/offcontrol may be provided by an isolated switch control circuit 180 thattakes low voltage control signals that are referenced to ground andconverts them to control signal referenced to 115 VAC. A voltage doublercircuit 179 converts the 115 VAC to approximately +280 VDC and −280 VDCfor use as capacitor charging voltages. The voltage doubler 179 iscapable of producing 320 VDC from 115 VAC. The actual voltage developedis controlled by the power regulator 190 and can vary between 250 VDCand 295 VDC.

The flash capacitors 178 are used to supply the energy used by theflashtube 34, 36. In a preferred embodiment, four capacitors may bearranged in two parallel sets that are connected in series. Theflashtube 34, 36, which may be a xenon gas flashtube, is connectedacross the series connected capacitors and provides a desired voltage ofabout 500 to 600 volts, for example, to the flashtube 34, 36.

More particularly, the anode and cathode of each flashtube 34, 36 isconnected to the outputs of the capacitors 178. In a preferredarrangement, the cathode of each tube 34, 36 is connected to the minuscapacitor through the secondary winding of the trigger inductor 100,102(transformer). The primary winding of the trigger inductor 100, 102 isconnected to a respective flashtube trigger generator circuit, therebeing a main flashtube trigger generator circuit 186 for the mainflashtube 34 and a spare flashtube trigger generator circuit 188 for thespare flashtube 36. When a trigger pulse, for example a −275 volt pulse,is applied to the primary winding of the trigger transformer, a highvoltage negative pulse, for example −5000 V to −7000 V, is developed bythe transformer secondary winding. This voltage causes the xenon gas inthe flashtube 34, 36 to change from an insulator to a low resistanceconductor, whereupon the flash capacitors 178 discharge through theflashtube 34, 36 creating a brilliant white flash of light. A groundedwire may be wrapped around the outside of the flashtube 34, 36 to helppropagated the ionization gas in the flashtube 34, 36 and provideshielding for EMI generated by the flashtube 34, 36 when it fires. Thisminimizes cross-talk between the main and spare flashtubes 34, 36. Also,this method of triggering the flashtubes 34, 36 provides several otheradvantages. In particular, it permits the flashtubes 34, 36 to bemounted in close proximity to one another in stacked relationship which,in turn, allows the common reflector 38 to be used for both flashtubes34, 36. As a consequence, the optical design of the reflector 38 andlens 20 is greatly simplified. Another advantage is that series triggercircuits provide trigger voltage isolation between flashtubes 34, 36 sothat trigger coupling between the closely spaced flashtubes 34, 36,which typically causes erratic flashing in parallel trigger circuits, isprevented. The series trigger circuit also provides electromagneticshielding for the flashtubes 34, 36 which reduces electromagneticinterference (EMI) that the flashtubes 34, 36 are exposed to duringinitial triggering. It also reduces the amount of EMI suppressionrequired to meet FAA imposed EMI requirements.

The charging of the flash capacitors 178 is controlled by a powerregulator 190. After a flashtube 34, 36 fires and the flash capacitors178 are discharged, the regulator 190 receives a timing signal from aflasher timer 192 to start charging the capacitors 178. The regulator190 supplies a signal to the isolated switch control 180 that is used toturn-on the transistor AC switch 179, starting the charging cycle. Afterthe capacitors 178 have been charged to the voltage needed to obtain therequired power, the power regulator 190 turns off the signal to theisolated switch control 180 which turns off the AC power to the flashcapacitors 178. As the capacitors 178 age and their capacitance changes,the power regulator 190 adjusts the capacitor charging voltage to keepthe power output constant, which output is a function of the flashcapacitor capacitance and the capacitor voltage. This keeps power at aminimum level and extends the life of the flashtube 34, 36. When theflashtube intensity decreases below the minimum threshold, an intensitymonitor power boost latch 194 (FIG. 6) sends a signal to the powerregulator 190 to increase the power to the flashtube 34, 36. This willincrease the intensity and provide additional operating time for theflashtube 34, 36 as was discussed above.

The regulator 190 preferably has associated therewith an over voltagemonitor 196 that measures the positive and negative flashtube voltages.If the charging voltage increases above a specified amount, for example,plus or minus 300 VDC, the over voltage monitor 196 overrides the powerregulator 190 with a turn-off signal to the isolated power controlcircuit 180. This would occur, for example, if the flashtube 34, 36 doesnot fire. In such event, the power regulator 190 would attempt to chargethe already charged capacitors 178 and would, if not stopped by the overvoltage monitor 196, overcharge the capacitors 178, and this may reducetheir useful life.

As further shown in FIGS. 5 and 6, the electrical circuitry includes async circuit 198 that supplies a sync signal, for example a 400 Hzsignal, to the flasher timer 192. This signal is used to control alltiming functions in the power supply 176 via the flasher timer 192 whichgenerates timing signals required by the power regulator 190 and thetrigger generators 186, 188. The timer 192 also generates a timingsignal for control of an intensity monitor circuit 200 that is discussedbelow. The trigger generators 186, 188 are capable of producing aflashtube trigger at a normal rate of 42 flashes per minute for example,and at least the spare trigger generator 188 is capable of producing aflashtube trigger at a different rate such as twice the normal rate or adouble flash trigger signal.

The power for the flashtube triggers 186, 188 is provided by a triggerpower circuit 202. The trigger power circuit 202 may be a positivevoltage doubler for supplying 300 VDC to the flashtube triggergenerators 186, 188. Each flashtube generator 186, 188 produces, forexample, a −275 volt pulse that is connected to the trigger coil of thetrigger transformer 100, 102 for the flashtube 34, 36. The pulse may begenerated by a capacitor discharge SCR circuit that is controlled by thelamp intensity monitor trigger control circuit 204, 206. If theflashtube 34 fails to fire, the capacitor voltage will be at a steadyvalue, either low or high depending on the cause of the flash notfiring. A flash detector 207 monitors the charging and discharging ofthe flash capacitors 178. If they are at a steady voltage and not beingcharged and discharged for a predetermined time period, the flashdetector 207 generates a fail signal that is sent to a main flashtubefail latch 208 to initiate the switching to the spare flashtube 36.Similarly, the spare flashtube generator 188 produces, for example, a−275 volt pulse that is connected to the secondary trigger coil of thetrigger transformer 102 for the spare flashtube 36. The pulse may begenerated by a capacitor discharge SCR circuit that is controlled by aspare lamp intensity monitor trigger control circuit 206.

As further seen in FIG. 5, the power supply 176 further comprises a lowvoltage power supply 209 for supplying low DC voltage to the flasherpower supply circuit and intensity monitor circuit. The low voltagepower supply 209 may include a transformer that steps the 115 VAC downto the desired DC voltages such as ±10 VDC and ±5 VDC. The transformermay also have an isolated winding that provides power to the isolatedswitch control circuit 180.

Referring now principally to FIG. 6, the intensity monitor and controlcircuit 166 includes a photodiode circuit 210 including the photodiode162 which as above noted continuously monitors the light intensity ofthe operating flashtube 34, 36 via the light pipe 156. The photodiodecircuit 210 provides an output signal to an integrator circuit 212 thatis proportional to the light intensity generated by the then operatingflashtube 34, 36. As is preferred, the photodiode 162 is selected toproduce a response that approximates the response of the human eye andto quantify the light intensity in candela, a photometric measurementallowing the intensity to be compared to requirements for FAA approvedintensity photometric test measurements. The photodiode 162 should alsobe capable of providing a stable output over the full operatingtemperature range of the flashtubes 34, 36. If the output of thephotodiode circuit 210 or alternative light sensor is temperaturesensitive, then temperature compensation could be provided to provide anormalized output. As is preferred, the photodiode 162 may be packagedin a metal hermetically sealed case with a glass window forenvironmental protection.

The integrator circuit 212 converts the measured light intensityprovided by the photodiode circuit 210 into an integrated output voltagewhich is a function of the light intensity of the flash emitted byflashtube 34, 36. Since the light intensity of the flashes typicallyvaries by a small amount, the light from multiple flashes is integratedto obtain an average intensity. Averaging the light intensity frommultiple flashes provides a more stable signal for the determination ofthe actual light intensity output and prevents a false lamp fail signalfrom being generated as a result of occasional sub-threshold flash. Eachtime the flashtube 34, 36 flashes, the integration output voltage willincrease by an amount proportional to the intensity of the flash. Thus,the voltage obtained at a particular time is equal to the total voltageof all the flashes measured up to that particular time. Thus, the outputsignal of the integrator 212 is a DC voltage proportional to the averageintensity of the light output. After a prescribed number of flashes havebeen integrated, the output of the integrator 212 is compared by anintensity comparator 214 against a reference value provided by areference voltage source 216 and then the integrator 212 is reset (tozero) by the intensity monitor counter 200 before measuring a nextseries of flashes.

The intensity comparator 214 monitors the output of the integrator 212and produces an output indicative of whether the integrator 212 outputsatisfies or does not satisfy the comparison criteria. In theillustrated embodiment, the comparator 214 produces a GO or NOGO signalbased on a comparison of the integrator 212 output signal to a referencevoltage preferably supplied by the reference voltage source 216 whichmay be a stable temperature compensated voltage circuit. The referencevoltage level may be set in relation to the FAA's minimum effectivelight intensity requirement, for example to correspond to the FAA'sminimum effective light intensity requirement or slightly above suchminimum requirement. If the integrator 212 output voltage is less thanthe reference voltage, the comparator 214 outputs a NOGO signal. If theintegrator 212 output voltage is greater than the reference voltage, thecomparator 214 outputs a GO signal.

Initially the integrator 212 output voltage will be below the comparatorreference voltage and the comparator 214 will output a NOGO signal. Asconsecutive light flashes are measured, the integrated output voltagewill gradually increase from zero volts to the final voltage measuredfor the prescribed number of flashes. When the integrator 212 outputvoltage rises above the reference voltage, the comparator 214 willoutput a GO signal. If the intensity of the flashtube 34, 36 decreasesbelow the minimum limit, the comparator output will stay in a NOGOstate.

After a set of flashes have been measured, the state of the comparatoroutput is stored in an intensity status latch circuit 220 which iscontrolled by the intensity monitor counter circuit 200. The intensitymonitor counter 200 is clocked by the flasher timer 192 and providestiming signals not only for the intensity status latch 220, but also forthe integrator 212, a light warm-up inhibit latch 222 and an intensityintegrator fail counter 226. At power turn-on the counter is set to zeroby a power-on reset circuit 225 and synchronizes the operation of thecounter.

After the intensity monitor counter 200 counts the prescribed number offlashes for a set of flashes to be integrated for comparison to thereference value, the counter 200 sends a clock signal to the intensitystatus latch 220 to have it store the GO/NOGO state of the intensitycomparator output. This occurs shortly before the counter 200 resets theintegrator 212, setting it to measure another set of flashes. The latch220 then ignores the comparator output until the next set of multipleflashes is measured and another clock signal sent by the counter 200 tothe intensity status latch 220.

Preferably the intensity status latch 220 is inhibited from outputting aNOGO signal for a preset period of time after the then active flashtube34, 36 has been turned on. This allows the flashtube 34, 36 to warm upto its operating temperature. Under some low temperature conditions, thelight intensity of the flashtube 34, 36 may be below the requiredintensity in which case a NOGO signal would be outputted by thecomparator 214 and captured by the intensity status latch 220 when,after a warm-up period, the light intensity would otherwise rise abovethe required minimum. An inhibit signal may be supplied from latch 222to the intensity status latch 220 for the prescribed period governed bythe intensity monitor counter 200, that is, the time period may be basedon a number of flashes needed to bring the flashtube 34, 36 up to itsoperating temperature.

The GO/NOGO status of the intensity status latch 220 is monitored by anintensity integrator fail counter circuit 226. The intensity integratorfail counter 226 prevents premature switching of the main flashtube 34to the spare flashtube 36 when the light intensity of the main flashtube36 approaches the minimum light intensity. Since the decrease in lightintensity usually is gradual, light output may intermittently fall belowthe specified minimum light intensity. The intensity integrator failcounter 226, which is clocked by the intensity monitor counter 200,monitors the intensity status latch 220 for a predetermined number ofconsecutive NOGO output signals corresponding to consecutive multiplesets of flashes. If the prescribed number of consecutive measurementsare NOGO, the intensity integrator fail counter 226 provides a failsignal in the form of a power boost latch set signal to the power boostlatch 194 which enables the power boost mode of the power regulator 190.In response, the power regulator 190 increases the voltage to which theflash capacitors 178 are charged. The increased voltage corresponds toan increase in the light intensity of the main flashtube 34. This, ineffect, extends the useful of the main flashtube 34. Moreover, thisextends the lifetime of the main flashtube 34 beyond the life the mainflashtube 34 would otherwise have had if operated at the higher voltage,as the lifetime of a flashtube typically decreases with increasingoperating voltage.

After the power to the main flashtube 34 is boosted, the intensityintegrator fail counter 226 continues to monitor the GO/NOGO status ofthe intensity status latch 220. If several consecutive measurements areNOGO, the intensity fail counter 226 provides a main lamp fail signal toa main lamp fail latch 208 for initiating switching to the spareflashtube 36. The main lamp fail latch 208 provides an inhibit signal tothe main lamp trigger control 204 and an enable signal to the spare lamptrigger control 206 (during operation of the main flashtube 34 the mainlamp fail latch 208 outputs an inhibit signal to the spare lamp trigger206 to prevent the spare flashtube 36 from flashing). The main lamp faillatch 208 also provides a reset signal to the power boost latch 194which causes the power regulator 190 to charge the flash capacitors 178to the original or normal power settings. The spare flashtube 36 willnow be flashed in place of the main flashtube 34.

During flashing of the spare flashtube 36, the intensity integrator failcounter 226 continues to monitor the GO/NOGO status of the intensitystatus latch 220 and the output of the intensity integrator fail counter226 is sent to a spare lamp fail latch circuit 228. If severalconsecutive measurements are NOGO, the intensity integrator fail counter226 provides a lamp fail signal to the power boost latch 194 whichenables the power boost mode of the power regulator 190. In response,the power regulator 190 increases the voltage to which the flashcapacitors 178 are charged. The increased voltage corresponds to anincrease in the light intensity of the spare flashtube 36. This, ineffect, extends the useful life of the spare flashtube. Moreover, thisextends the lifetime of the spare flashtube beyond the life the spareflashtube would otherwise have had if operated at the higher voltage.

After the power to the spare flashtube 36 is boosted, the intensityintegrator fail counter 226 continues to monitor the GO/NOGO status ofthe intensity status latch 220. If several consecutive measurements areNOGO, the intensity fail counter 226 provides a spare lamp fail signalto the spare lamp fail latch 228 which sends a double flash enablesignal to the spare lamp trigger 206. The spare flashtube 36 is thendouble flashed to provide a visible indication to the air crew and/orground maintenance personnel that the intensity of the light is near theFAA minimum level. In the preferred embodiment, the spare flashtube 36flashes at 84 flashes per minute, which is twice the 42 flashes perminute in normal operation. Preferably, during double flashing, everyother flash is generated at reduced power to limit the total power tothe flashtube to a level that will not cause the flashtube to overheatand burn-out. Notably, both the normal (42 FPM) and the double (84 FPM)flash rate fall within the FAA's acceptable flash rate range. The“double flash” rate alerts aircraft maintenance personnel that the lightintensity of the anti-collision light 10 is near the minimum requiredeffective intensity and that servicing of the anti-collision light 10 isrequired. The spare flashtube 36 will continue to double flash untilrepaired or replaced. As is preferred, battery power is provided whenthe light 10 is turned off to retain the low intensity status untilpower is reapplied.

After both lamps have reached their end-of-life, it may be desirable toflash both lamps simultaneously to generate sufficient light output fromthe light fixture. This may require some redundancy such as two sets offlash capacitors.

An operating hours counter circuit 230 counts the number of flashes thathave been accumulated by the flashtubes 34, 36. The counter 230 isclocked by the flasher timer 192 and increments each time a flashtube34, 36 fires. As is preferred, the counter 230 is powered from batterypower and retains its count when the light 10 is not powered. In apreferred embodiment, the counter 230 is capable of recording about26,000 hours of operation (about 67 million flashes) and can only bereset during maintenance when the flashtubes 34, 36 are replaced.

Although the invention has been shown and described with respect tocertain preferred embodiments, equivalent alterations and modificationswill occur to others skilled in the art upon reading and understandingthis specification and the annexed drawings. In particular regard to thevarious functions performed by the above described integers (components,assemblies, devices, compositions, etc.), the terms (including areference to a “means”) used to describe such integers are intended tocorrespond, unless otherwise indicated, to any integer which performsthe specified function of the described integer (i.e., that isfunctionally equivalent), even though not structurally equivalent to thedisclosed structure which performs the function in the hereinillustrated exemplary embodiment or embodiments of the invention. Inaddition, while a particular feature of the invention may have beendescribed above with respect to only one of several illustratedembodiments, such feature may be combined with one or more otherfeatures of the other embodiments, as may be desired and advantageousfor any given or particular application.

What is claimed is:
 1. A recognition light for an aircraft, comprising:a flashtube; a flash capacitor connect d to the flashtube; a powerregulator for changing the flash capacitor to a first voltage levelprior to being discharged through the flashtube; a light detectorpositioned to detect light emitted from the flashtube; a monitor circuitconnected to the light detector for measuring the intensity of thedetected light, comparing the measured intensity with a reference valuecorresponding to a predetermined light intensity level, and outputting asignal when a specified relationship exists between the measuredintensity and the reference value that indicates a need to increase thelight intensity of the flashtube; and a control circuit connected to thepower regulator and monitor circuit which causes the power regulator, inresponse to said signal from the monitor circuit, to charge the flashcapacitor to a second voltage level higher than said first voltage levelprior to being discharged through the flashtube, whereby the flashtubeinitially operates at a first power level and then at a second higherpower level.
 2. A method for increasing the useful life of a recognitionlight of an aircraft, comprising: flashing a flashtube by repeatedlycharging a flash capacitor to a first voltage and discharging thecapacitor through the flashtube; monitoring the light output of theflashtube; comparing the measured light output of the flashtube with areference value corresponding to a predetermined light intensity value;increasing the voltage to which the flash capacitor is charged to asecond voltage higher than the first voltage when a specifiedrelationship exists between the measured light output and the referencevalue that indicates a need to increase the light intensity of theflashtube, thereby to increase the intensity of the flashes emitted bythe flashtube.
 3. A method for increasing the useful life of arecognition light of an aircraft, comprising: flashing a flashtube;monitoring the light output of the flashtube; comparing the measuredlight output of the flashtube with a reference value corresponding to apredetermined light intensity value; increasing the power delivered tothe flashtube when a specified relationship exists between the measuredlight output and the reference value indicates a need to increase thelight intensity of the flashtube, thereby to increase the intensity ofthe flashes emitted by the flashtube; and providing a second flashtubeoperative to flash at a rate different than that of the first flashtube.4. The method of claim 3, further comprising operating the secondflashtube in place of the first flashtube when the measured light outputof the first flashtube falls below a specified level.
 5. The method ofclaim 3, further comprising monitoring the light output of the secondflashtube and, when the light output of the second flashtube falls belowa specified level, causing the second flashtube to flash at a ratedifferent than that which he first flashtube flashed.
 6. A method formonitoring the useful life of an aircraft recognition light, comprising:flashing a flashtube; monitoring the light output of the flashtube witha light detector that converts the detected light output into anintegrated output voltage corresponding to the light output of aplurality of flashes of the flashtube; providing an intensity comparatorfor comparing the integrated output voltage to a comparator referencevoltage; comparing the integrated output voltage to the comparatorreference voltage and, if the integrated output voltage is less than thecomparator reference voltage, transmitting a NOGO condition signal, and,if the integrated output voltage is greater than the comparatorreference voltage, transmitting a GO condition signal; storing thecondition signal in an intensity status latch; providing an intensityintegrator fail counter for monitoring the GO/NOGO condition signal ofthe intensity status latch for a predetermined number of consecutivedecreases and transmitting a boost signal or fail signal in responsethereto; monitoring the GO/NOGO condition signal and, if thepredetermined number of consecutive NOGO measurements is attained,transmitting a boost signal for initiating an increase in powercorresponding to an increase in the light output of the first flashtube;and providing a second flash tube operative to flash at a rate differentthan that of the first flashtube, and continuing monitoring the GO/NOGOcondition signal of the intensity status latch and, if the predeterminednumber of NOGO measurements is attained, transmitting a fail signal forinitiating operation of the second flashtube at a rate substantiallysimilar to the rate of the first flashtube.
 7. The method of claim 6,further comprising using the intensity integrator fail counter formonitoring a GO/NOGO condition signal associated with the secondflashtube and, if the predetermined number of NOGO measurements isattained, transmitting a boost signal for initiating an increase inpower corresponding to an increase in the light output of the secondflashtube.
 8. The method of claim 7, further comprising continuingmonitoring the GO/NOGO condition signal associated with the secondflashtube and, if the predetermined number of NOGO measurements isattained, transmitting a fail signal for causing the second flashtube toflash at the different rate.
 9. A recognition light for an aircraft,comprising first and second flashtubes; and circuitry for operatingeither one of the first and second flashtubes at a first power level andlater for operating at least one of the flashtubes at a second higherpower level when the light intensity of said one of the flashtubes fallsbelow a specified level, and wherein at least one of the first andsecond flashtubes is flashed at a first rate when operated at the firstpower level and at a second flash rate when operated at the secondhigher power level.